A METHOD  FOR  MEASURING  THE 
DENSITY  OF  MOLTEN  GLASS 

BY 

GORDON  KLEIN 


THESIS 

FOR  THE 

DEGREE  OF  BACHELOR  OF  SCIENCE 

IN 

CERAMIC  ENGINEERING 


COLLEGE  OF  ENGINEERING 


UNIVERSITY  OF  ILLINOIS 


1921 


\^2.\ 


UNIVERSITY  OF  ILLINOIS 


February...  5 19  £1.. 

•ns 

O 

THIS  IS  TO  CERTIFY  THAT  THE  THESIS  PREPARED  UNDER  MY  SUPERVISION  BY 

GO 

GORDON .KLEIN 

ENTITLED A. . JMG5.X  N.QL . . .E  OR . . ME  AS.U.HINC- . . .THE . . DELI.b.I  I Y. . . .05! . . M.OL.TE  N. . .GLASS 


IS  APPROVED  BY  ME  AS  FULFILLING  THIS  PART  OF  THE  REQUIREMENTS  FOR  THE 
DEGREE  OF BA.CHE.L0B. 0J. SCIENCE. 


HEAD  OF  DEPARTMENT  OF... .0$ RAJ/LI .0. . . EN.G.I NEE R IN.G. 


' 


TABLE  OF  CONTENTS 


Page 


I.  INTRODUCTION  * 1 

II.  THE  METHOD  EMPLOYED 2 


III.  FIRST  EXPERIMENT  . . . 

IV.  SECOND  EXPERIMENT  . . 

V.  THIRD  EXPERIMENT  . . . 

VI.  FOURTH  EXPERIMENT  . . 

VII.  SUMMARY  AND  CONCLUSIONS 


7 

8 

13 

14 


4?6SS8 


Digitized  by  the  Internet  Archive 
in  2016 


https://archive.org/details/methodformeasuriOOklei 


/■  METHOD  FOR  MEASURING  THE  DENSITY  OF  MOLTEN  GLARE . 


I.  INTRODUCTION 

All  density  determinations  for  glass  have  been  made  at 
temperatures  below  the  sof tening  point . It  was  the  purpose  of 
the  present  investigation  to  determine  the  density  of  molten  glass 
at  temperatures  up  to  1400°  C. 

The  literature  on  the  determination  of  densities  of 
molten  liquids  at  high  temperatures  revealed  only  two  methods  of 
importance.  Both  were  applications  of  the  principle  of  Archimedes. 
Day,  Sosman  and  Hostetter,*  in  their  "Determination  of  Mineral  and 
Rock  Densities  at  High  Temperatures",  developed  a very  expensive 
and  elaborate  apparatus  which  was  only  fairly  satisfactory.  The 
other  work  was  by  F.  M.  Jaeger,**  who  determined  densities  from 
the  loss  in  weight  of  a pla.tinum  bob  (immersed  in  the  melt)  due 
to  the  buoyant  action  of  the  fluid  glass.  The  practical  applica- 
tion of  this  method  is  not  as  simple  as  it  at  first  appears,  and 
the  corrections  for  surface  tension  and  viscosity,  etc.,  necessary 
for  the  calculation  of  density  would  require  their  determinations. 


*Amer.  Jour,  of  Sci.  ser.4,  v. 37,  p.  1-39. 

**See  Uber  die  Temperaturabhangegkeit  der  molekularen  freien 
Oberf lachenergie  von  Fluesigkeiten  im  Temperaturbereich  von 
”80  bis  ~1650°C.,  by  Dr.  F.  M.  Jaeger. 


. 


II.  THE  METHOD  EMPLOYED 

After  due  consideration  of  the  experimental  difficulties 
and  opportunities  for  error  in  the  application  of  the  principle  of 
Archimedes,  it  was  decided  to  use  the  pycnometer  method,  i.e., 
the  determination  of  the  weight  of  a known  volume  of  liquid  glass. 

For  this  method  of  determination  the  procedure  is  as 
follows:  a pycnometer  of  known  volume  and  weight  is  evacuated  to 
a pressure  of  0.2  to  0.3  mm.  of  mercury,  and  sealed  off  in  such  a 
manner  that  the  vacuum  is  not  destroyed  until  the  pycnometer  is 
totally  immersed  in  the  liquid  glass.  The  temperature  of  the 
pycnometer  when  immersed  is  accurately  determined  by  some  suitable 
means.  When  filled, the  pycnometer  is  removed  and  the  weight  of 
the  glass  therein  determined.  From  the  calculated  volume  of  the 
pycnometer  at  the  filling  temperature  and  the  weight  of  the  glass 

maS  g 

therein,  the  density  is  obtained  by  the  equation,  density  = -^7^— 

The  pycnometer  must  be  constructed  of  a material  which 
has  the  following  properties:  (l)  melting  point  above  140C°C.; 

(2)  strength  and  rigidity  at  1400°  sufficient  to  retain  shape; 

(3)  known  coefficient  cf  expansion  up  to  14CO°C.;  (4)  ability  to 

resist  corrosive  action  of  melt  without  appreciable  change  in 
volume;  (5)  a non-wetting  surface  to  the  melt,  or  such  a different 
expansion  as  to  make  cleaning  the  pycnometer  easy  and  complete 
before  the  final  weighing.  The  cost  and  machining  properties 
are  also  important  considerations. 

The  properties  of  nickel  make  it  a desirable  material  for 
this  purpose.  There  has  been,  however,  no  accurate  determination 
made  of  its  linear  expansion  above  1C00°C. , but  it  was  decided  to 


3. 


use  the  values  given  in  Landolt,  Bornstein,  and  Roth,  a.s  determined 
by  C.  Holborn  and  Day*  between  3C0  end  1000°  C. , and  by  extrapolation 
calculate  the  expansion  at  the  higher  temperatures. 

Since  the  coefficient  of  expansion  of  nickel  is  la.rger 
than  that  of  glass,  the  pycnometer  on  cooling  will  either  rupture 
or,  if  the  glass  is  sufficiently  fluid,  the  pressure  will  eject  a 
small  quantity  of  it  from  the  opening.  If  liquid  glass  is  ejected 
provision  must  be  made  to  collect  it.  The  opening  thru  which  glass 
enters  the  cylinder  must  be  of  such  shape  that  it  can  be  quickly 
cleaned  off  when  taken  from  the  melt.  With  this  point  in  mind,  the 
first  pycnometer  was  designed  as  shewn  in  figure  I,  Plate  I.  The 
hole  in  the  riser  tube,  at  the  top,  thru  which  the  glass  enters  the 
cylinder  is  2 mm.  in  diameter.  This  size  was  determined  by  calcula- 
tion from  viscosity  values  determined  in  this  laboratory  for  a lead 
glass  at  1350°C.  This  diameter  is  sufficient  to  allow  the  pycnometer 
which  has  a volume  of  about  70cc. , to  fill  under  atmospheric  pres- 
sure in  30  minutes.  P copper  tube,  3/16  inches  in  diameter  and  20 
inches  long, was  braised  on  to  this  riser  tube  for  a double  purpose. 
First,  as  a means  by  which  the  pycnometer  could  be  sealed  off  when 
evacuated,  and  second,  to  afford  a means  of  breaking  the  vacuum 
seal  underneath  the  surface  of  the  glass  melt.  If  the  pycnometer 
is  pushed  quickly  under  the  surface,  the  seal  remains  intact  until 
the  copper  tube  melts.  The  pressure  of  the  atmosphere  will  then 
force  the  glass  into  the  pycnometer. 

The  pycnometer  was  evacuated  by  connecting  the  copper  tube 
to  a vacuum  line  by  means  of  a short  length  of  rubber  tubing.  When 
the  evacuation  was  completed,  a pinch- cock  was  clamped  on  the  rubber 
tubing.  In  order  to  see  if  the  pycnometer  was  holding  the  vacuum, 

* Ann . d .Phys . v.4  (4)  p.  104  (1901)  


' 


4. 


the  pinch-cock  was  unclamped,  and  the  action  of  the  manometer  in 
the  vacuum  line  observed.  Some  difficulty  was  encountered  in 
obtaining  a pressure  of  0.3mm.  but  by  filling  the  space  between 
the  top  and  cylinder  with  solder,  the  pycnometer  was  made  to  hold 
this  pressure  indefinitely.  This  use  of  solder  for  obtaining  a 
vacuum  tight  joint  is  not  to  be  recommended  however,  for  on  melting, 
some  of  the  solder  would  doubtlessly  flow  into  the  pycnometer  and 
change  its  volume. 

Volume  determinations  of  the  pycnometer  were  made  by 
dividing:  the  difference  in  weight  of  the  pycnometer  when  empty 
and  the  weight  when  filled  with  mercury,  by  the  density  of  mercury 
at  the  room  temperature. 


. 


PLATE  I. 


5. 


/C"'y  J1C  CSco/e.  F'fjZZ' 


6. 


III.  FIRST  EXPERIMENT 

In  the  first  experiment  the  melt  was  a lead  glass.  The 
glass  pot  was  about  10  inches  deep  and  had  a capacity  of  a little 
over  3 liters.  Temperature  readings  were  taken  with  a Fe"ry 
Radiation  pyrometer,  which  was  focused  on  the  surface  of  the  melt, 
so  that  the  temperature  observed  was  that  of  the  coldest  part  of 
the  melt.  The  temperature  was  first  raised  to  14C0°0.  and  held 
at  that  point  for  one  hour  to  free  the  melt  from  bubbles.  Then  at 
a surface  temperature  of  1380°,  the  pycnometer  wa.3  quickly  levered 
into  the  melt.  The  vacuum  seal  appeared  to  hold,  and  the  copper 
tube  came  off  as  was  expected.  The  temperature  was  held  at  1380° 
for  half  an  hour.  An  effort  was  then  made  to  lift  the  pycnometer 
from  the  pot  with  a pair  of  steel  tongs  but  the  tongs  softened  at 
this  temperature  and  a firm  grip  on  the  pycnometer  could  not  be 
obtained.  In  order  to  remove  the  pycnometer,  it  was  necessary  to 
take  the  pot  out  of  the  furnace  and  pour  out  the  molten  glass.  The 
pycnometer  came  out  in  four  pieces  . The  nickel  had  fractured  when 
it  was  plunged  into  the  glass. 

From  this  first  run,  although  unsuccessful,  several 
important  facts  were  learned.  First,  the  nickel  must  be  heated 
before  plunging  into  the  molten  glass.  Second,  the  surface  tempera- 
ture of  the  glass  in  such  a pot  lagged  behind  the  temperature  in  the 
bottom  by  about  15C°C.  A close  examination  of  the  pycnometer  frag- 
ments revealed  evidences  of  melting.  Third,  a cradle  or  support  by 
which  the  pycnometer  could  be  lowered  into  and  taken  from  the  melt 
was  necessary.  Furthermore,  the  use  of  solder  tc  make  the  pycno- 
meter vacuum  tight  is  undesirable,  because  the  solder  vaporizes  at 

these  high  temperatures  filling  the  glass  and  pycnometer  with  its 
gases . 


' 


7. 


IV.  SECOND  EXPERIMENT 

The  equipment  in  this  experiment  was  substantially  the 
same  as  that  in  the  first.  The  only  changes  were  the  cradle,  in 
which  the  pycnometer  rested  while  in  the  melt,  and  the  addition  of 
a copper  gasket  a.t  the  point  A in  Fig.  .II,  Plate  I.  This  gasket 
eliminated  the  necessity  for  the  use  of  solder.  The  Fery  Radiation 
pyrometer  was  again  used  for  temperature  determinations,  but  the 
surface  temperature  in  this  experiment  was  held  at  1250°  C.  It 
was  estimated  that  the  temperature  2 inches  below  the  surface,  the 
level  to  which  the  riser  tube  came,  was  at  least  50°  higher.  The 
pycnometer  was  heated  to  a cherry  red,  and  at  that  temperature  was 
lowered  into  the  melt.  After  30  minutes,  during  which  time  the 
temperature  was  held  constant,  the  cradle  and  pycnometer  were  lifted 
from  the  pot.  Examination  of  the  pycnometer  revealed  that  it  had 
hot  filled  with  glass.  No  doubt  the  vacuum  had  been  destroyed  when 
the  pycnometer  was  heated  before  plunging  into  the  melt.  As  all 
possible  care  had  been  taken  with  this  operation,  it  was  decided 
that  the  arrangement  used  tc  seal  off  the  pycnometer  was  not 
practical,  and  that  some  radical  change  in  design  and  method  of 
procedure  were  necessary  if  results  were  to  be  obtained  with  this 
method . 

The  preheating  of  the  nickel,  however,  did  eliminate  the 
danger  of  the  pycnometer  breaking  when  it  was  lowered  into  the 
melt.  Nickel  proved  itself  a desirable  material  for  pycnometer 
construction  as  it  cleaned  easily  and  thoroughly. 


. 


8. 


V.  THIRD  EXPERIMENT 

In  view  of  the  difficulties  encountered  in  the  first  two 
experiments,  it  was  decided  that  a change  in  method  was  neceasary. 
For  this  reason  a new  method  was  devised  which  was  a3  follows: 
a small  electrically  heated  pot  furnace  containing  the  pycnometer 
and  glass  was  put  under  a large  metal  bell  jar  capable  of  being 
evacuated  to  a pressure  of  less  than  1.0  mm.  of  mercury.  (See 
Plates  II  and  III.)  The  temperature  of  the  glass  pot  was  then 
gradually  raised,  and  at  the  same  time  the  pressure  in  the  bell  jar 
gradually  reduced.  When  the  molten  glass  had  become  practically 
free  from  occluded  gases,  and  had  reached  the  desired  temperature, 
the  vacuum  was  broken  and  the  glass  was  forced  into  the  pycnometer 
under  a pressure  of  one  atmosphere.  The  pycnometer  was  then  removed 
and  weighed  as  outlined  in  the  preceding  experiments.  Fig.  II 
shows  the  arrangement  thru  which  the  pot  and  pycnometer  could  be 
observed  while  under  the  bell  jar.  This  was  necessary  in  order 
that  the  progress  of  the  fining  operation  could  be  observed. 
Results  obtained  by  this  method  would  give  the  density  of  practi- 
cally gas-free  glass. 

This  new  method  necessitated  a change  in  the  design  of 
the  pycnometer.  The  riser  tube  was  eliminated  and  the  top  made  of 
one  solid  piece.  The  opening  was  enlarged  to  4mm.  in  diameter. 
Provision  for  lifting  the  cylinder  from  the  pot,  was  made  by  means 
of  a nickel  rod,  hooked  at  one  end  and  threaded  at  the  other  end 
which  screwed  into  tile  base  of  the  pycnometer.  (See  Fig.  Ill, 

Plate  I . ) 


PLATE  II. 


Note  . The  tank  £ is  not  a part  of  the 
equipment.  The  coil  to  the  right  of  the 
tank  is  the  heating  coil  rheostat. 


‘».:k  •>' 


eo 


= — 

PL£  TE  III. 


10. 


11. 

The  pot  was  heated  by  passing  a current  thru  a platinum 
coil  which  was  wound  on  the  outside  of  the  alundum  cylinder  in  which 
the  pot  rested.  Temperature  was  determined  by  means  of  a thermo- 
couple  of  platinum  and  platinum-rhodium  alloy,  the  hot  junction  of 
which  was  between  the  outer  wall  of  the  pot  and  the  inner  wall  of  the 
alundum  cylinder,  midway  between  the  top  and  bottom  of  the  pot. 

PI  ate  IV.  is  cross-section  view  of  the  furnace  used  if  the  pot  dimen- 
sions are  changed  to  3 1/4"  wide  and  7 1/2 " high.  The  platinum  heat- 
ing coil  should  be  shown  as  circling  the  alundum  or  refractory  cement 
It  was  checked  by  means  of  a Leeds-Nor thrup  optical  pyrometer,  which 
was  sighted  on  the  surface  of  the  melt. 

The  pot  and  pycnometer  are  shewn  in  Fig.  Ill,  Plate  I. 

It  will  be  observed  from  the  figure  that  the  pycnometer  opening  is 
near  the  bottom  of  the  pot.  The  pycnometer  rested  upon  two  nickel 
pellets,  which  raised  the  opening  at  least  a quarter-inch  from  the 
bottom  of  the  pot.  When  the  pycnometer  was  lifted  from  the  pot  in 
this  inverted  position,  atmospheric  pressure  on  the  opening  held 
the  glass  in  the  cylinder. 

One  run  with  this  arrangement  revealed  its  most  serious 
defect.  No  matter  how  carefully  the  temperature  and  pressure  were 
controlled,  gases  coming  out  of  the  glass  and  the  nickel  were  certain 
to  be  trapped  in  the  upper  part  of  the  pycnometer.  This  resulted  in 
a partially  filled  cylinder  . 

The  method  of  lifting  the  cylinder  from  the  pot,  and  all 
other  arrangements  were  satisfactory,  with  the  exception  of  heat  dis- 
tribution and  temperature  control.  The  surface  temperature  of  the 
glass  as  determined  by  the  optical  pyrometer  lagged  150  degrees  be- 
hind the  temperature  at  the  thermo-couple  junction.  No  doubt  the 

temperature  in  the  bottom  of  the  pot  was  also  considerably  higher 
than  that  at  the  thermo-couple. 


_ 


, 

■ 


12. 


PLATE  IV. 


13. 


VI.  FOURTH  EXPERIMENT 

The  pycnometer  shown  in  Fig.  IV,  Plate  I,  was  made 
especially  for  this  experiment.  The  sloping  top  facilitates  the 
escape  of  any  gases  liberated  in  the  pycnometer.  The  flat  platform 
serves  a double  purpose,  in  that  it  affords  a means  of  collecting 
all  glass  ejected  on  cooling,  and  can  be  gripped  by  a pair  of  tongs. 

A lead  glass  was  also  used  in  this  run.  It  was  fined  by 
alternately  increasing  the  temperature  and  diminishing  the  pressure. 
Fining  was  considered  complete  when  no  more  gas  bubbles  could  be 
seen  in  the  glass.  The  pressure  had  been  reduced  to  0.3mm.  and  the 
temperature  increased  to  1350°C.  when  the  fining  was  considered 
complete.  During  the  fining  process,  gas  bubbles  could  be  seen 
arising  from  the  opening  in  the  pycnometer,  which  showed  that  the 
sloping  cap  was  functioning  as  expected.  Care  must  be  taken  not  to 
reduce  the  pressure  toe  quickly  or  the  occluded  gases  will  cause  the 
glass  to  froth  and  run  over  the  sides  of  the  pot.  When  fining  was 
complete  the  vacuum  was  broken.  The  glass  then  sank  to  a new  level. 
In  a few  minutes  the  level  was  still  lower,  and  a glance  at  the 
ammeter  in  the  heating  coil  circuit  showed  a short  circuit  in 
that  line.  The  bottom  of  the  pot  had  failed,  due  to  the  corrosive 
action  of  the  lead  glass  and  the  weight  of  the  pycnometer.  Further- 
more the  temperature  at  the  bottom  must  have  been  considerably  high- 
er than  that  at  the  thermo-couple,  for  the  nickel  on  the  bottom  of 
the  pycnometer  had  melted.  It  is  al30  possible  that  at  this  high 
temperature  lead  from  the  glass  formed  a low  temperature  alloy  with 
the  nickel.  The  entire  cylinder  showed  evidences  of  corrosion,  and 
had  the  appearance  of  having  been  exposed  to  the  action  of  lead 


vapor . 


- 


. 


■ 

■ 

■ 

• . 


14. 


Tiiis  experiment  showed  the  necessity  of  some  arrangement 
whereby  the  temperature  of  all  parts  of  the  pot  could  be  measured. 

^s  no  more  time  was  available  the  work  was  discontinued 
at  this  point . 

VII.  SUMMARY  AND  CONCLUSIONS 

Although  unsuccessful  in  accomplishing  the  main  purpose 
of  the  investigation,  a few  facts  have  been  ascertained  which  are 
worthy  of  notice: 

(1)  A nickel  pycnometer  is  not  suitable  for  work  with 
lead  glasses,  but  would  probably  be  satisfactory  for  ether  glasses. 

(2)  The  design  of  the  pycnometer  used  in  the  last 
experiment  is  satisfactory  and  is  recommended. 

(3)  The  actual  temperature  of  the  glass  in  the  pycnometer 
should  be  measured. 


In  conclusion  I wish  to  thank  Professor  E.  W.  Washburn 
for  suggesting  this  work  and  for  his  kind  interest  and  suggestive 
criticism  during  its  progress.  I am  also  indebted  to  Dr.  E.  N. 
Bunting  for  his  help  and  guidance  in  the  laboratory. 


